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Recitation 4: glycolysis, gluconeogenesis, and the citric acid cycle Bi/Ch 110 November 16, 2016 Announcements • Revised office hours: • Camille: Weds 1-2pm SFL 229 • Emily: Fri 4-5pm SFL 229 • Due dates: • Pset 4 due Tues, Nov 22 • Pset 5 going out Tues Nov 22, due Dec 1 Agenda • Questions about Pset 3? • Review of metabolism thus far • Practice problems • Questions about Pset 4? Basics of metabolism • ATP is the cell’s energy currency • Catabolism: turning carbon fuels into ATP • glycolysis, the citric acid cycle • Fuel CO2 + H2O + energy • Metabolism: using energy from ATP • Synthesis of fats, amino acids, nucleotides and complex biological molecules • ΔG must be negative for the entire set of reactions Where does the energy come from? • Oxidation of carbon atoms goes through a high-phosphoryl-transferpotential compound, which is then used to generate ATP • Electrons from oxidation are transferred to an activated carrier such as NAD+ • Oxidation of more complex fuels happens one carbon at a time What carries the electrons? What carries the electrons? Overview of catabolism Overview of catabolism Glycolysis Overview of catabolism Citric Acid Cycle Reactions of glycolysis • Glucose is imported into cytoplasm via transport proteins • First phosphorylation traps glucose in the cell • Isomerization and phosphorylation ensures that aldol cleavage creates two interconvertible three-carbon molecules Reactions of glycolysis • Oxidation of aldehyde generates NADH and ATP • Shift of phosphoryl group creates a high phosphoryl-transfer potential because phosphoenolpyruvate is trapped in the unstable enol form rather than the stable ketone Overall reaction of glycolysis glucose + 2 NAD+ + 2 Pi + 2 ADP 2 pyruvate + 2 NADH + 2 H+ + 2 ATP + 2 H2O Keeping redox balance Anaerobic The fate of pyruvate in aerobic respiration: acetyl CoA • Pyruvate dehydrogenase complex converts the output of glycolysis (pyruvate) into the input for the citric acid cycle (acetyl CoA) • Takes place in the mitochondrial matrix • Produces one NADH The citric acid cycle • Takes place in the mitochondrial matrix • Works on 2-carbon units • Begins with transfer of acetyl group onto oxaloacetate and ends with regeneration of oxaloacetate after release of 2 CO2 Overall reaction of the citric acid cycle acetyl CoA + 3 NAD+ + FAD + Pi + ADP + H2O CoA + 3 NADH + FADH2 + 2 H+ + ATP + 2 CO2 Gluconeogenesis • Turns non-carbohydrate precursors into glucose • Lactate (recycled from anaerobic respiration) • Amino acids • Glycerol • Precursors enter in as pyruvate (lactate, aa’s), oxaloacetate (aa’s) or dihydroxyacetone phosphate (glycerol) • Takes place in the liver to regulate blood glucose levels Gluconeogenesis is not a reversal of glycolysis Reactions of gluconeogenesis • Unique reactions shown in red • Overall reaction: 2 pyruvate + 4 ATP + 2 GTP + 2 NADH + 6 H2O glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+ + 2 H+ Which reactions should be regulated? Which reactions should be regulated? Metabolic regulation • Typically the irreversible steps • How? • Controlling amounts of enzymes via transcription • Controlling catalytic activity via allostery or covalent modification • Energy sensors: ATP/ADP/AMP, NAD+/NADH • Products • Downstream molecules • Controlling availability of substrates Glycolysis and gluconeogenesis are reciprocally regulated Practice Problems Practice question 1 a) What makes ATP such a useful cellular “energy currency”? b) Based on the table, which direction will the following reactions run given equimolar amounts of reactants? i. ATP + creatine creatine phosphate + ADP ii. ATP + glycerol glycerol 3-phosphate + ADP Practice question 1 a) What makes ATP such a useful cellular “energy currency”? It has an intermediate phosphoryl-transfer potential so it can act both as a phosphoryl donor and acceptor for important biomolecules. See textbook Figure 15.6, page 430. b) Based on the table, which direction will the following reactions run given equimolar amounts of reactants? i. ATP + creatine creatine phosphate + ADP Forward reaction: -30.5 kJ/mol Reverse reaction: -43.1 kJ/mol ii. ATP + glycerol glycerol 3-phosphate + ADP Forward reaction: -30.5 kJ/mol Reverse reaction: -9.2 kJ/mol Practice question 2 If glucose is labeled with 14C on the C2 carbon circled below, where does that label end up if the end product of metabolism is ethanol? Practice question 2 If glucose is labeled with 14C on the C2 carbon circled below, where does that label end up if the end product of metabolism is ethanol? Practice question 3 Explain why your muscles feel sore/burning after intense exercise. Practice question 3 Explain why your muscles feel sore/burning after intense exercise. After intense exercise, muscle tissue will run out of oxygen. Therefore, the muscle cannot use aerobic respiration (citric acid cycle and oxidative phosphorylation) to regenerate ATP and instead must use anaerobic respiration. The product of anaerobic respiration is lactate, or lactic acid, which produces a burning sensation in the muscle due to low pH. Practice question 4 How much ATP would be generated from each of the following molecules if it were processed fully to lactate? a) Glyceraldehyde 3-phosphate b) Fructose Practice question 4 How much ATP would be generated from each of the following molecules if it were processed fully to lactate? a) Glyceraldehyde 3-phosphate 2 ATP b) Fructose 2 ATP Practice question 5 How many ATP/GTP molecules are needed to make glucose from each of the following precursors? a) Two molecules of oxaloacetate b) Fructose 1,6bisphosphate Practice question 5 How many ATP/GTP molecules are needed to make glucose from each of the following precursors? a) Two molecules of oxaloacetate 4 ATP/GTP a) Fructose 1,6bisphosphate 0 ATP/GTP Practice question 6 At equilibrium, 96% of the triose phosphate is dihydroxyacetone phosphate rather than glyceraldehyde 3-phosphate. However, the reaction to produce glyceraldehyde 3-phosphate proceeds. Why? Practice question 6 At equilibrium, 96% of the triose phosphate is dihydroxyacetone phosphate rather than glyceraldehyde 3-phosphate. However, the reaction to produce glyceraldehyde 3-phosphate proceeds. Why? The rest of the reactions of glycolysis use up glyceraldehyde 3-phosphate, removing the product of the reaction and therefore driving it forward.